Bacterial adherence to the host tissue is recognized as a key step in the development of a bacterial infection. In the present proposal the extracellular connective tissue matrix rather than membrane components of the host cell is considered as a substrate for bacterial adherence and colonization. Recent studies in our and other laboratories which show that certain bacteria produce distinct cell wall components that specifically bind to fibronectin will be taken as a starting point for the proposed investigation. The structures of sites in the fibronectin molecule binding to model strains of Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli will be determined. To this end the protein will be cleaved by the use of proteolytic enzymes and CNBr. Generated peptides will subsequently be isolated and their ability to bind to bacteria or inhibit the binding of intact 125I-fibronectin to bacteria will be examined. The bacterial receptors responsible for fibronectin binding will be isolated and characterized. Different techniques will be tried to solubilize the fibronectin receptors which subsequently will be purified using affinity chromatography on Sepharose gels substituted with fibronectin or active fibronectin fragments in combination with conventional protein fractionation techniques. The isolated receptors will be characterized with respect to chemical and immunological properties. Specifically monoclonal antibodies will be raised against the receptor component and monoclonals that block the binding of I-fibronectin to bacteria will be searched for. The role of fibronectin in bacterial adherence will be examined. A model system consisting of coverslips coated with fibronectin or fibroblasts cultured in vitro will be used as substrates for adherence of fibronectin binding bacteria as well as receptor negative mutants. Attempts will be made to inhibit adherence by preincubating the bacteria with A) soluble fibronectin and its active fragments and B) monoclonal antibodies directed against the fibronectin receptors.